Can you have a CEL with no corresponding DTC? It's on an '88 F150 w/ the 302 and a manual trans. I have a CEL and DTCs but the CEL doesn't seem to correspond with the DTCs.

I have pulled codes multiple times over the past couple of weeks and keep getting 33 and 44 on the KOER (11 for KOEO and CM though I've had others recently which I've resolved) which should be for EGR and the secondary air system. The problem is that I can get my CEL to go off by disconnecting the wire from the coolant temperature sending unit and that makes no sense to me since there's no DTC for the coolant system.

I have recently replaced the coolant temperature sending unit, the coolant temperature sensor, and parts of the coolant bypass system (the hose and one of the nipple it connects to). So my question then becomes is this an issue with the coolant system, is this an electrical issue, or something else entirely?

I can't even imagine how I still have a code 33 either since I've tested the harness, replaced the EGR valve, put on a new EVP sensor (I'm using the old one at the moment b/c the new one is throwing a code 34), tested the voltage and continuity of the wiring harness for the EVP sensor, and I patched a hole in the EGR line, but I guess I can deal with this in another thread since this shouldn't be causing my CEL, right?

 

You might have a small vacuum leak some where throwing the codes.

 

At the moment I'm getting 53 KOEO but I've tested the voltage at both the ECT and TPS sensors and am getting about 12 volts so that's definitely not good. I'm going to test the computer and VREF voltage from the source since the shop manual is leading me to that pinpoint test.

I definitely have a vacuum issue but I don't know that it's a leak. The issue seems to be HVAC related and deals with the white vacuum line under the hood that connects to a vacuum pump/motor in the extreme rear corner of the passenger side of the engine compartment (above the A/C components). When I move the actuator arm on the vacuum pump/motor I can hear what sounds like the blend door opening and closing. But -- and here's the interesting part -- if I disconnect that white vacuum line from the pump/motor and give it constant vacuum from another source then I can get full HVAC controls but if I reconnect that line properly then I can only get air out of the defroster and floor vents. I can't figure out for the life of me what the two have to do with each other but for right now I've got a line running from the cruise control vacuum connector port on the intake manifold since I don't have cruise control and I need A/C blowing out of the panel vents. The only problem with this is that when I open the throttle too much too quickly or have the engine speed really high for a while I can't seem to get enough vacuum to keep it blowing out the panel vents and some times it takes quite a while to get it back. I have no idea if this related to my other problem but that's probably in part because I have no idea what exactly either of my problems (electrical and vacuum) are at the moment .

 

Oh and for the vacuum issue, I cannot find that part of the system on the diagram in the engine compartment or in the Ford Vacuum & Electrical Troubleshooting Manual so I have no idea where I could find information on that system from. I have also looked in my shop manuals and can't really find anything on it either but I might not be looking for the right thing.

 

The reason the flow from the dash vents cuts off when under load is there's no vacuum accumulator in the system the way you have it connected.