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'87 Suburban TBI Problems

On a recent trip I was cruising along at about 70mph. The check engine light came on and I noticed that there were some minor performance issue. However upon slowing down the engine began to stutter considerably. It know sits in my drive way with several failed attempts at repair. Symptoms are as follows:

1)Revs and surges but fails to idle smoothly to the point of dying. 2)I am able to drive it if I constantly pump the throttle to gain speed. At higher speeds I can drive down the road. 3)Runs rough and acts like it is running rich. 4)Code scanning returns a 44 which is a "lean" condition even though acts as "rich"

5)Oddly if I remove the electrical connection from the MAP sensor, it will idle fine and rev smoothly while NOT under load. Under load it still hesitates but I am able to drive it and once I hit about 60mph the problem seems to go away...hopefully not to a dealer which I can't afford.

I have made the following repairs with no success:

1)New fuel filter 2)New 02 sensor 3)New Coolant Sensor 4)New MAP sensor 5)New TBI gasket 6)New Plugs 7)New Vacuum hoses and checked for vacuum leaks 8)New PCV 9)IAC operating normally 10)New MAP & Throttle Position Sensor tested "ok" at a major car parts store.

I had read some posting relating to Quad-Drivers and the ECM stating that 87 TBI were known to have some problems.

Any comments to cuase would be greatly appreciated.

Reply to
J.P. Burton
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Well, taking it to someone to have it scanned and diagnosed costs about

40 bucks around here. Heck of a lot cheaper than all the following good parts you threw at it.

Given that list, that leaves the distributor (including cap, rotor, and spark module), the Computer, and a poor connection on the coolant sensor as my most likely guesses. The coolant sensor you replaced was the one in the intake, just to the side of the thermostat, correct? The one in the side of the head is for the gauge. A faulty injector can also cause something similar. Pull off the air cleaner and look to see they are both firing. Have the spark module tested.

Unrelated. The quad drivers are high current transistors, built so they can be paralleled for higher current applications. On the 87, they run the torque convertor lock up (two of them paralleled), the EGR solenoid, and the third escapes me right now. But that's not the problem with your truck.

Keep all the old parts for your truck. Most were probably good. If the spark module tests ok, bring it to a local shop. Even the tune up places will be able to diagnose it for you for 50 bucks or less.

Lastly, you say it acts like it's running rich. Is it putting out black smoke? Your symptoms sound lean to me, which would negate what I said above and make me look at fuel delivery restriction of some kind. Start with looking at the injectors. If the patterns are a nice inverted cone shape, and they both look the same, then move on to the next step.

Reply to
John Alt

I don't think it's anything but an EGR. Pop it off and clean it, post your results.

~KJ~

Reply to
KJ

Hell yeah, this has EGR written all over it. I'd bet $50 and a case of beer that's what it is.

Doc

Reply to
"Doc"

I'm getting pretty good at back seat diagnosis by the looks of it. LOL

~KJ~

Reply to
KJ

Should I jack around with the EGR Solenoid?? Also when I had the MAP disconnected and was idling in park (perfectly) I could feel some movement of the EGR upon revving the engine but I am not sure of the travel. I guess potentially the port is clogged. It just seemed very strange that I could run it, to an extent, with the MAP disconnected. I never have had a TBI vehicle before let alone anything that was so "controlled" by an ECM. If it is the EGR I would have my sister come visit you...if I had one.

"Doc" wrote in news:H%lPb.3271$ snipped-for-privacy@news1.news.adelphia.net:

Reply to
J.P. Burton

This sounds so similar to my recent problem that I had to check the name on the post. Mine turned out to be a bad fuel injector that operated like this intermittently for about two months and then died altogether. It also gave me a code 44 - you might want to check your fuel injectors when it's acting up at idle.

Reply to
Rich B

EGRs cause problems at idle and at roadway speeds. When you get on the highway it stops using the EGR and will run just fine. I had a

4-banger 88 S10 that had a absolutley broken (in two) EGR and would run on the highway.

~TLGM

Reply to
Lonely G-Monkey

cruising on the highway is *exactly* when the EGR is called for. EGR isn't used at idle or WOT. the reason a vehicle with a malfunctioning (usually leaking) EGR does better on the highway is because the EGR would be in use anyway, negating the leak.

-Bret

Reply to
Bret Chase

If it's the original EGR, I guarantee you it's shot. It might not be causing your driveability issues, but it's shot nonetheless! For your truck it's about $60.

Doc

Reply to
"Doc"

How are you so sure? I have what I'm sure is the same engine in my 87 van. I took mine off for cleaning not long ago and it looked relatively pristine. The diaphragm tested ok too.

CJ

Reply to
CJBrown

Thank you very much for correcting me. I must have had a brain skid, hopefully the OP will check back here and find my mistake. I found a good write up of the exact workings of an EGR valve.

EGR Theory. EGR serves one purpose and one purpose only. That purpose is to reduce Oxides of Nitrogen (NOx). Undernormal combustion, Nitrogen(N2)Oxygen (O2) in the air and Hydrocarbons (HC) in the fuel combind into water(H2O) Carbon dioxide (CO2) and the Nitrogen remains unchanged. Under very hot combustion temperatures, the Nitrogen reacts with the other two byproducts and forms Nitrogen oxide (NO). After being released into the atmosphere, it picks up another Oxygen and becomes Nitrogen dioxide (NO2). In the presence of sunlight, it combines with other compounds like Hydrocarbons and forms Smog. Since exhaust gas is inert (very stable) it doesn't burn again. So by being introduced into the combustion chamber, it will lower combustion chamber temps enough so that the Nitrogen doesn't react with the other compounds and is passed unchanged out the tailpipe thus not contributing to smog. Now, since exhaust gas doesn't burn, it doesn't exactly help with combustion. At higher RPM's, this really isn't noticable, but at idle, the reintroduction of exhaust gas will cause a very rough idle and can cause stalling if to much is introduced into the combustion chamber

~KJ~

Reply to
KJ

Hey J.P.

Did you find the problem? Just reading your post sounds just like the problem I had with my 92 burb and it was the fuel pump.

Reply to
Tim H.

================================= Maybe I missed it but, does it have vacuum to the ?MAP?

Reply to
Scott M

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